The present invention is related to threading closures and, more particularly, to threading cylindrical-walled metal closures. Such closures include metal caps which are commonly used on a variety of bottles and jars such as mayonnaise jars, cosmetic containers, medicine bottles, and the like. The metal cap threaded in accordance with the invention consists of a metal shell having a cylindrical wall. The screw threads are formed inwardly on the cylindrical wall.
Various methods are known for threading caps. One of the first methods of threading metal caps utilized two expanding tools in series. The first tool formed segments of threads leaving intervening unthreaded areas, and the second tool completed the thread.
Another method of threading caps is shown in U.S. Pat. No. 2,209,416 issued to Montelione. In this method a rotating chuck was utilized to hold a cap, and a threading tool smaller than the cap was inserted into the cap. After inserting the threading tool into the cap, the tool was moved toward the wall of the cap to form the thread by impressing a pre-threaded portion on the threading tool into the edge of the cap which had previously been turned inwardly. The threading tool would rotate in the same direction as the cap rotated. Furthermore, the threading tool rotates at the same speed as the cap. Such threading equipment necessitates removal of the cap from the cap-forming apparatus and movement to the threading station where the cap must be rotated during the threading operation.